Power converters such as DC-to-DC voltage converters, DC-to-AC power inverters, and the like, generally use one or more power switching transistor devices and one or more magnetic storage elements in the power conversion process. Examples of such converters are: buck converters, boost converters, forward converters, and flyback converters. Such power converters generally have control circuitry for operating the switching transistors and generally use the magnetic storage elements to store, transfer, and/or transform power from an input source to an output source. Many of these converters have two power switching transistors operating in an anti-phase relationship to one another. Specifically, one such switching transistor usually operates to couple power to the magnetic storage element from the input power source while the other switching transistor may be used to recycle surplus stored energy in the magnetic storage element back to the input supply. Alternately, as a second example, the second switch may act as a synchronous rectifier on the secondary side of the magnetic storage element. Such power converters typically provide conversions at power levels of 50 W and above. The power switching transistors in such converters are relatively large devices in comparison with general-purpose transistors and, therefore, have relatively high gate capacitances.
Typically, these power transistors are switched at frequencies of 250 kHz to 2 MHz. Given this relatively high frequency for power transistor devices and the relatively high gate capacitances, switching power converters generally have large heavy-duty drive circuits for switching these power transistors. Such a drive circuit may typically comprise a large high-powered buffer amplifier and an isolation transformer coupled between the buffer amplifier and power transistor through one or more blocking capacitors. Additionally, as noted above, many power converters have two such power switching transistors operating in an anti-phase relationship, thus requiring two such transistor drive circuits. However, one of the two switching transistors usually does not require a corresponding isolation transformer because it and its corresponding drive circuit operate in the same range of voltage. In such cases, only one of the two drive circuits will require an isolation transformer and corresponding blocking capacitors.
Due to increases in operating frequency and improvements in magnetic storage elements, switching power converters have now evolved to the point that the commonly-used power transistor drive circuits occupy substantial "board" area (or cubic volume) of the power converter and add significant costs to the manufacturing of such power converters. Therefore, there is a significant need in the switching-power supply industry to reduce the costs and "board" area of these circuits.